The lipoxygenases are a structurally related family of non-heme iron dioxygenases that function in the production of fatty acid hydroperoxides. Three lipoxygenases have been identified and cloned in humans. Funk, C. D. (1993) Prog. Nuc. Acid Res. Mol. Biol. 45:67-98; Matsumoto et al. (1988) Proc. Natl. Acad. Sci. USA 85: 26-30; Dixon et al. (1988) Proc. Natl. Acad. Sci. USA 85: 416-420; Funk et al. (1990) Proc. Natl. Acad. Sci. USA 87: 5638-5642; Izumi et al. (1990) Proc. Natl. Acad. Sci. USA 87:7477-7481; Yoshimoto et al. (1990) Biochem. Biophys. Res. Comm. 172:1230-1235; Sigal et al. (1988) Biochem. Biophys. Res. Comm. 157:457-464). They oxygenate arachidonic acid in different positions along the carbon chain and form the corresponding 5S-, 12S- or 15S-hydroperoxides (hydroperoxy-eicosatetraenoic acids, HPETEs). The three enzymes are known mainly from the blood cell types in which they are strongly expressed--the 5S-lipoxygenase of leukocytes, the 12S-lipoxygenase of platelets, and the 15S-lipoxygenase of reticulocytes, eosinophils and macrophages. While these are the most widely recognized cellular sources, selective expression is well documented in other tissues. For example, both the 12S- and 15S-lipoxygenases are detected in skin. Nugteren et al. (1987) Biochim. Biophys. Acta 921:135-141; Henneicke-von Zepelin et al. (1991) J. Invest. Dermatol. 97:291-297; Takahashi et al. (1993) J. Biol. Chem. 268:16443-16448; Hussain et al. (1994) Amer. J. Physiol. 266:C243-C253.
Potentially, the three cloned lipoxygenases could account for all enzymatic synthesis of arachidonate hydroperoxides in humans, but there are reasons to consider that other lipoxygenases may exist. For example, in the mouse there are five known lipoxygenases, three that correspond to the known human enzymes, Chen et al. (1994) J. Biol. Chem. 269:13979-13987; Chen et al. (1995) J. Biol. Chem. 270:17993-17999 and two others, Furstenberger et al. (1991) J. Biol. Chem. 266:15738-15745; Funk et al. (1996) J. Biol. Chem. 271:23338-23344.
Three of the five distinct mouse lipoxygenase enzymes are best known for their occurrence in different types of blood cells. In common with other mammals, a 5S-lipoxygenase is present in leukocytes and is responsible for synthesis of the pro-inflammatory mediators, the leukotrienes. Chen et al. (1995) J. Biol. Chem. 270:17993-17999; Chen et al. (1994) Nature 372:179-182. A 12S-lipoxygenase is found in platelets and several other tissues including skin. Nugteren et al. (1987) Biochim. Biophys. Acta 921:135-141; Chen et al. (1994) J. Biol. Chem. 269:13979-13987; Sun et al. (1996) J. Biol. Chem. 271:24055-24062.
A second type of 12S-lipoxygenase which is closely related in sequence to the human and rabbit "reticulocyte-type" of 15S-lipoxygenases occurs in certain macrophages. Sun et al. (1996) J. Biol. Chem. 271, 24055-24062. The fourth mouse lipoxygenase to be characterized is another enzyme to have 12S-lipoxygenase activity; it was cloned recently from mouse skin and has been classified as an epidermal 12S-lipoxygenase. van Dijk et al. (1995) Biochim. Biophys. Acta 1259:4-8; Funk et al. (1996) J. Biol. Chem. 271:23338-23344. All four of these murine lipoxygenases enzymes have been characterized at the cDNA and genomic levels.
The fifth known mouse lipoxygenase was described originally in 1986 by Furstenberger, Marks and colleagues as an enzyme in skin forming 8-HETE and inducible by phorbol ester treatment. Gschwendt et al. (1986) Carcinogenesis 7:449-455. It was shown subsequently that this enzyme forms the 8S enantiomer (Hughes et al. (1991) Biochim. Biophys. Acta 1081:347-354) and isolation of the corresponding hydroperoxide confirmed identification of the enzyme as a lipoxygenase. Furstenberger et al. (1991) J. Biol. Chem. 266:15738-15745. Mouse skin is the only reported site of synthesis of 8S-HETE in animal tissues, and there is no indication from the literature pointing to a potential homologue of the mouse 8S-lipoxygenase in other mammals. Additionally, no nucleic acid, particularly a cDNA, which encodes this lipoxygenase has been characterized.
Despite the description in the art of the enzymes presented above, along with the catalytic activities covered by these enzymes, there remains an open question whether a lipoxygenase rather than a cytochrome P450 might account for the synthesis of 12R-hydroxy arachidonic acid (12R-HETE), Hammarstrom et al. (1975) Proc. Natl. Acad. Sci. USA 72:5130-5134; Woollard, P. M. (1986) Biochem. Biophys. Res. Commun. 136(1):169-175; Baer et al. (1991) J. Lipid Research 32:341-347; Holtzman et al. (1989) J. Clin. Invest. 84:1446-1453; Brash et al. (1996) J. Biol. Chem. 271:20549-20557, a prominent arachidonate metabolite in the skin disease of psoriasis and other proliferative dermatol (Hammarstrom et al. (1975) Proc. Natl. Acad. Sci. USA 72:5130-5134; Baer et al. (1991) J. Lipid Research 32:341-347; Baer et al. (1995) J. Invest. Dermatol. 104:251-255).
Therefore, what is needed, then, is further characterization of lipoxygenase enzymes in vertebrates, particularly in mammals, and more particularly in humans. A novel isolated and purified lipoxygenase and a nucleic acid encoding the same would have broad utility to due its role in arachidonic acid metabolism, a critical metabolic pathway.